(1) Field of the Invention
The present invention relates to a biochemical analyzer analyzing an amount of a component included in a sample, and more particularly to a biochemical analyzer analyzing an amount of a component included in a subject's blood or urine.
(2) Description of Related Art
As the analyzing apparatus analyzing the amount of a component included in a sample, there is a widely used analyzing apparatus which irradiates a light from a light source to a reaction solution in which a sample and a reagent are mixed, and measures an amount of transmitted light having one or more specific wavelengths so as to calculate an absorbance, and determining the amount of the component on the basis of a Lambert-Beer's law (for example, patent document 1 (U.S. Pat. No. 4,451,433)).
In the automatic analyzer, it is necessary to measure an amount of light with respect to many wavelengths corresponding to a number of analytical items. In the automatic analyzer, there has been a light transmitting member transmitting a plurality of dispersed monochromatic lights, a light receiving element array having a light receiving element receiving the monochromatic light passing through the light transmitting member, and a light receiving element array integrally formed in the light transmitting member (for example, patent document 2 (JP-A-6-229829)). Further, there has been a light shielding means which is arranged between a reaction tube and a diffraction grating placed away in a direction of an optical axis of the light transmitting through the reaction tube, and is provided with a through port passing a predetermined range of lights around the optical axis in the transmitted or scattered light (for example, patent document 3 (JP-A-2005-49109)).
FIG. 1 shows a main structure of an automatic analyzer of the prior art for measuring an amount of component included in blood or urine. The automatic analyzer is constituted by a sample cup 2 accommodating a sample 1 in an inner portion, a sample disk 3 in which a plurality of sample cups 2 are arranged, a reagent cup 5 accommodating a reagent 4 in an inner portion, a reagent disk 6 in which a plurality of reagent cups 5 are arranged, a cell 8 mixing the sample 1 and the reagent 4 in an inner portion so as to form a reaction solution 7, a cell disk 9 in which a plurality of cells 8 are arranged, a sample dispensing mechanism 10 which can move the sample 1 from an inner side of the sample cup 2 to an inner side of the cell 8 at a fixed amount, a reagent dispensing mechanism 11 which can move the reagent 4 from an inner side of the reagent cup 5 to an inner side of the cell 8 at a fixed amount, a mixing unit 12 mixing the sample 1 and the reagent 4 within the cell 8, a measuring unit 13 irradiating a light from a light source 15 to the reaction solution 7 so as to disperse the transmitted light and measure an amount of light per wavelength by a light receiving element array 21, a cleaning unit 14 cleaning the cell 8, a control portion controlling each of the apparatus portions mentioned above, a data storage portion storing various data, an input portion which can input a necessary data in the data storage portion from an outer portion, a measuring portion calculating an absorbance from the amount of light, an analyzing portion determining an amount of component from the absorbance, and an output portion which can display the data and can output to the outer portion.
An analysis of an amount of a certain component present in the sample 1 is carried out in accordance with the following procedure. First, the sample 1 within the sample cup 2 is dispensed at a fixed amount into the cell 8 by the sample dispensing mechanism 10. Next, the reagent 4 within the reagent cup 5 is dispensed at a fixed amount into the cell 8. Subsequently, the sample 2 and the reagent 4 within the cell 8 are mixed by the mixing unit 12 so as to form the reaction solution 7. If necessary, a plurality of reagents 4 are additionally dispensed into the cell 8 by the reagent dispensing mechanism 11. The amount of the transmitted light from irradiating the reaction solution 7 is measured by the measuring unit 13, the absorbance is calculated in the measuring portion, and the absorbance data is accumulated in the date storage portion. After the end of the reaction, the inner side of the cell 8 is cleaned by the cleaning mechanism 14 and the next analysis is carried out. In the analyzing portion, the amount of the component is analyzed from the accumulated absorbent data on the basis of an analytical curve data and the Lambert-Beer's law. Data necessary for control and analysis is input to the data storage portion from the input portion. Various data and the results of analysis are displayed and output by an output portion.
FIG. 2 shows a structure of a known conventional measuring unit 13 and measuring portion. A light 16 emitted from the light source 15 is focused by a lens 17, passes through a slit 19a, transmits through the reaction solution 7 and thereafter enters into a dark box 18. The dark box 18 is light shielded so as to prevent the other lights than the light passing through a slit 19b from being incident. The light 16 is dispersed per wavelength by a light dispersing portion 20 after passing through the slit 19b, and enters into the light receiving element array 21. The light receiving element array 21 is connected to a measuring portion. A structure of a known conventional light receiving element array 21 is shown in FIG. 3. A plurality of light receiving elements 22 receiving different wavelengths of the dispersed light are discretely installed on a base table 27. A silicone diode is generally used in the light receiving element 22. In this case, there is shown an example in which twelve light receiving elements 22a to 22l are arranged for receiving twelve different wavelengths of light. A front surface of the light receiving element 22 is provided with a mask 24 for removing a reflected stray light and a color glass filter 25 via a spacer 23. Each of the light receiving elements 22a to 22l is connected to the measuring portion, and transmits a photoelectric current value which is in proportion to the amount of the received light to the measuring portion. The measuring portion converts the photoelectric current value into the absorbance.
In this case, if the amount of the detected light received by the light receiving element 22 is equal to or less than a fixed amount, the precision of the absorbance analysis is lowered by noise such as a dark current or the like except for the photoelectric current. Accordingly, it is necessary to set the amount of the light received by each of the light receiving elements to a fixed amount or more. In the automatic analyzer, it is often the case that the wavelength region from about 340 nm to about 800 nm is used, and a halogen lamp is used for the light source. FIG. 4 is a graph showing a wavelength dependency of the light amount of the halogen light source. As can be appreciated from FIG. 4, in an ultraviolet region which is shorter than 400 nm the light amount becomes small.
In order to increase the analysis precision to a fixed level or higher, it is necessary to design an optical system within the measuring unit in such a manner that a fixed amount or more of light can be secured in the ultraviolet region. In order to secure a light amount equal to or more than the fixed level, it is important to set an acceptance angle (hereafter load angle) of the light received by the light receiving element which is large. A load angle α is shown in FIG. 2. The load angle α is decided by a light beam view showing a state in which the light source is assumed as a point light source and a light emitted from the point light source reaches the light receiving element. For example, as shown in FIG. 2, the load angle is decided by adjusting a distance between an image forming point on which the lights from the point light source converge and a slit 19a, and a width ‘a’ of the slit 19a. In this case, the load angle in the present specification does not take an influence by a chromatic aberration of a lens or the like into consideration. It is more advantageous to secure the light amount equal to or more than a fixed level in accordance with an increase of the load angle. In this case, in the analysis items of the automatic analyzer, there is an analysis item of scattering the light by using a particle or the like, measuring the amount of the transmitted light other than the scattered light and calculating the absorbance. In the case mentioned above, since an accurate measurement can not be carried out if the light receiving element receives the scattered light, it is necessary that the light receiving element does not receive the scattered light.
It is advantageous for increasing the light amount to make the load angle α larger, however, the scattered light tends to be loaded as well. If the scattered light is loaded, the light receiving element receives extra light, so that a measurable concentration range narrows. In other words, there is a problem that a dynamic range of the measurable concentration decreases. Accordingly, it is important to remove the scattered light in the same manner as securing the light amount. With regard to the problem of the scattered light removal, for example, there is mentioned in patent document 3 a method relating to a removal of a scattered light by a slit. However, in accordance with this method, the load angle becomes small, and there is a problem that it is hard to secure the light having the wavelength in which the light amount is small. From the fact mentioned above, there is needed a method of removing the scattered light while securing a fixed amount or more of the light amount.
As mentioned above, there is a problem that if the load angle is made larger for increasing the light amount, the scattered light is easily loaded, and if the load angle is made smaller for removing the scattered light, the light amount becomes small.